The original comment seemed to trivialize the differences between the games. If you wanted to you could say something similar about any conditional branch but doing so completely ignores the differences between the branches. Assemble time checking for _RED and _BLUE makes it easy to switch between versions sure, but the it doesn't say anything about the actual differences (large or small) between the versions. A simple flag like that can be used to build vastly different programs. Also, given that those flags are macros to begin with tells me we don't even know if that was how the originals were differentiated; you can't really disassemble a macro.
edit: I don't mean to be an ass about this. There's certainly a sort of poetic quality to the use of a flag like that to switch between versions but I just thought it was worth also pointing out the work it took to do so.